Field of the Invention
One aspect of the present invention relates to a driver of a vibrator, a method of driving the same, a lens driver, a vibration device, and an imaging device.
Description of the Related Art
Vibration-type actuators in a system that applies an alternating current signal to an electro-mechanical transducer to obtain driving force in a vibrating body, and drives a lens of a camera, a video, or the like have been proposed by the applicant of the present invention, and the like.
FIG. 16 is a perspective view of an appearance illustrating an example of a basic configuration of the conventional vibration-type actuator.
As illustrated in FIG. 16, a vibrator of the vibration-type actuator includes an elastic member 4 made of a metal material formed into a rectangular plate, and a piezoelectric element (electro-mechanical transducer) 5 is joined to a back surface of the elastic member 4.
One obtained such that the elastic member 4 and the piezoelectric element 5 are affixed and integrated is referred to as vibrator. Here, a plurality of projection portions 6 is provided at predetermined positions on an upper surface of the elastic member 4.
FIG. 17A and FIG. 17B are diagrams illustrating secondary bending oscillation in a long side direction of the elastic member 4 of the vibration-type actuator and primary bending oscillation in a short side direction of the elastic member 4.
Here, the secondary bending oscillation in the long side direction is referred to as A mode (See FIG. 17A), and the primary bending oscillation in the short side direction is referred to as B mode (See FIG. 17B).
According to the above-described configuration, when the alternating current voltage is applied to the piezoelectric element 5, the A mode and the B mode are generated at the same time, and elliptical motion is excited in the projection portions 6.
Then, a driven body 7 is brought into pressure-contact with the projection portions 6, whereby the driven body 7 can be linearly driven by the elliptical motion of the projection portions 6. That is, the projection portions 6 functions as a driver unit of the vibrator.
FIG. 18 is a diagram illustrating an electrode pattern of the piezoelectric element 5, and electrode areas that are two equal portions divided in a longitudinal direction (X direction) are formed. Further, polarization directions in the respective electrode areas are the same direction (“+”).
An alternating current voltage (V1) is applied to an A electrode area positioned on the right side of FIG. 18, and an alternating current voltage (V2) is applied to a B electrode area positioned on the left side, of the two electrode areas of the piezoelectric element 5.
In FIG. 18, the right-side electrode area of the piezoelectric element 5 is contracted and the left-side electrode area is expanded at a certain moment, where the V1 and V2 are the alternating current voltages having a frequency in the vicinity of a resonant frequency of the A mode, and having phases shifted by 180°.
Further, the two electrode areas have an inverse relationship at another moment. As a result, vibration of the A mode illustrated in FIG. 17A is generated in the vibrator.
Further, the entire piezoelectric element 5 (the two electrode areas) is expanded at a certain moment, and is contracted at another moment, where the V1 and V2 are the alternating current voltages having a frequency in the vicinity of a resonant frequency of the B mode, and having the same phase.
As a result, vibration of the B mode illustrated in FIG. 17B is generated in the vibrator. As described above, each vibration in the vibrator is combined, whereby the moving body brought into pressure-contact with the projection portions 6 is driven in the arrow direction of FIG. 16. Further, an occurrence ratio of the A mode and the B mode can be changed by changing of the phase difference of the voltages to be input to the two equally divided electrodes.
A configuration and a driving principle of such a vibration-type actuator are described in Japanese Patent Application Laid-Open No. 2004-320846, and the like, and thus description is omitted.
Note that the vibrator is a vibration generation section in which the elastic member and the piezoelectric element are affixed, the vibration-type actuator is a portion that generates driving force that brings the vibrator and the moving body into pressure-contact and moves the moving body, and a vibration-type actuator device includes at least one or more of the driving force portions, and the driving force is provided to a moving portion, whereby rotary motion or linear motion becomes possible.
FIG. 19 is a diagram illustrating a relationship between a speed and consumption power of the actuator with respect to a drive frequency when driving and controlling the vibration-type actuator.
In control of the vibration-type actuator, speed control of measuring the speed of the pressurized and frictionally driven moving body, decreasing the frequency and increasing the speed when the detected speed is lower than a target speed, and increasing the frequency to a higher frequency and decreasing the speed when the detected speed is larger than the target speed is performed.
As a characteristic of the vibration-type actuator, when the drive frequency is lowered, input electric power is increased and an output is also increased.
Here, a relationship between the speed and the consumption power when a load is increased is illustrated by the dotted line. It can be seen that the speed is zero, that is, the actuator cannot be started at the dotted line of the drive frequency.
Under this state, when the frequency is decreased until the actuator is started, the actuator cannot be started and becomes non-start, or a phenomenon occurs, in which the actuator is started at a sharp speed at a frequency decreased from the drive frequency.
As described above, even if the actuator can be started, the actuator rises at a sharp speed, and smooth start becomes difficult. Further, the input electric power when started becomes large, and may become larger than set allowable electric power.
Further, while a state in which a load becomes large has been described above, a similar phenomenon occurs when startability is degraded due to variation or degradation of the vibrator.